To satisfy demands for wireless data traffic having increased since commercialization of 4th-Generation (4G) communication systems, efforts have been made to develop improved 5th-Generation (5G) communication systems or pre-5G communication systems. For this reason, the 5G communication system or the pre-5G communication system is also called a beyond-4G-network communication system or a post-Long Term Evolution (LTE) system.
To achieve a high data rate, implementation of the 5G communication system in an ultra-high frequency (mmWave) band (e.g., a 60 GHz band) is under consideration. In the 5G communication system, beamforming, massive multi-input multi-output (MIMO), full dimensional MIMO (FD-MIMO), an array antenna, analog beamforming, and large-scale antenna technologies have been discussed to alleviate a propagation path loss and to increase a propagation distance in the ultra-high frequency band.
For system network improvement, in the 5G communication system, techniques such as an evolved small cell, an advanced small cell, a cloud radio access network (RAN), an ultra-dense network, a device to device (D2D) communication, a wireless backhaul, a moving network, cooperative communication, coordinated multi-points (CoMPs), and interference cancellation have been developed.
In the 5G system, advanced coding modulation (ACM) schemes including hybrid frequency-shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and sliding window superposition coding (SWSC), and advanced access schemes including filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) have been developed.
Meanwhile, due to the recent emergence of Internet of Things (IoT), a D2D communication technology has attracted more attention as one of communication methods for interworking with smart devices. The D2D communication technology works based on physical proximity between user equipments (UEs), and has many advantages in terms of network resource efficiency increase, UE power consumption reduction, cellular communication area expansion, and so forth. In line with this, the 3rd-Generation Partnership Project (3GPP) has selected the D2D technology as a study item in the Release 12 and has carried out feasibility study on the D2D technology in the name of the Proximity-based Service (PreSe) since 2011, and has launched standardization activities in earnest since 2013.
During D2D communication, a transmission D2D UE transmits data packets to a group of D2D UEs or broadcasts data packets to all D2D UEs. D2D communication between a transmitter and receiver(s) essentially corresponds to a non-connection. That is, before the transmitter starts transmission of data packets, there is no connection configuration between the transmitter and the receiver. During transmission, the transmitter inserts a source identification (ID) and a destination ID into the data packets. The source ID is set as a UE ID of the transmitter. The destination ID corresponds to a broadcast ID or a group ID of the receiver to receive the transmitted packet.
One of the D2D communication requirements is to make an out-of-coverage remote UE communicate with a network through another UE (that is, a network-relay or relay UE) that is within the network coverage and is close to the remote UE. The relay UE playing a relay role is referred to as a ‘UE-to-Network relay’. Herein below, the relay UE and the ‘UE-to-Network relay’ will be used together. The remote UE communicates with a network-relay UE through D2D communication.
FIG. 1 illustrates an example of communication of a remote UE with a UE-to-Network relay by using D2D communication.
Referring to FIG. 1, a remote UE 100 communicates with a network through a UE-to-Network relay 110 and is a UE that is within a network coverage and intends to communicate with the network through the UE-to-Network relay 110.
D2D communication is performed between the remote UE 100 and the UE-to-Network relay 110, and cellular communication is performed between the UE-to-Network relay 110 and an evolved NodeB (eNB) 120.
The eNB 120 is connected to a public safety server (hereinafter, referred to as a “server”) 140 through an evolved packet core (EPC) 130. The EPC 130 means a network system configured with an EPC, which is an Internet protocol (IP)-based packet switched (PS) core network and an access network such as LTE/Universal Terrestrial Radio Access Network (UTRAN), etc., and also means an evolving network of a Universal Mobile Telecommunication System (UMTS).
There is no mechanism for prioritizing or differentiating relay packets in comparison to non-relay packets on a radio link between the UE-to-Network relay 110 and the eNB 120. Relay traffic is intended for public safety. However, relay traffic generated in a relay UE may not be intended for public safety, or the relay UE may relay packets from remote UEs having different priorities. In this case, radio-level quality of service (QoS) differentiation is required.